The invention relates to electrical switches and, in particular, to switches having at least one stationary contact made of highly conductive material preferably nobel metal being supported by an electrically isolating support and furthermore comprising at least one counter contact spring for operating with said stationary contact and being arranged such that this contact spring rests on the isolating support when the electrical switch is in its open position.
If it is desired to switch low voltages and a small current and to achieve a very small contact or transition resistance in the closed position of the switch the engaging contact surfaces have to be made of a material that conducts well. If it is required that the low transition resistance even for a long time is not increased by oxidation or other impairing effects on the surface properties of the contact material in practice only nobel metals such as gold can be used as contact material. Gold, however, is a relatively soft material so that with such contacts a removal by scratching or wearing of contact material may arise, particularly if the contact springs engage each other under strong tension. This in many cases is required if the switch is required to be vibration and shockproof. If, in the course of operating the switch, contact material is removed by the contact spring and is deposited on adjacent parts of the support, the isolating resistance of the switch is decreased in an uncontrolled manner. This, in particular, when small currents and low voltages have to be switched, leads to interference and falsification of signals.
It is an object of the invention therefore to provide a switch of the kind as stated above in which, in spite of using relatively soft contact material, and in spite of relatively high contact pressure being applied, any reduction of isolating resistance caused by wearing away of contact material is safely avoided. These and other objects are solved by the invention as characterized in the appending claims. By providing the isolating support with a recessed portion behind the contact, eventual contact wear will be collected within said recess portion or pocket. Since with the switch in the open position the contact spring does not rest on the recessed portion of the isolating support but on elevation portions extending in parallel to the pocket and since no contact wear can be moved to said elevated portion, the high isolating resistance between the stationary and the counter contact spring will not be impaired by eventual deposits of metal due to contact wear. The switch is characterized by a relatively simple structure and a high long-term reliability.